如何对具有嵌套数组/字典的 NSArray 和 NSDictionary 进行真正的深度复制？

Question

问题：有没有一种方法可以使用现有的 Objective-C 方法来对 NSDictionary 或 NSArray 进行完整的深层复制，而它们本身也有嵌套的字典或数组？

也就是说，我读到问题可能是当它遇到嵌套字典或数组时，它仅复制指向嵌套项目的指针，而不是真正复制该项目。

背景：作为我的一个例子，我尝试使用 NSUserDefaults 加载/保存以下配置，并且在加载时需要将从 NSUserDefault 获取的不可变副本转换为可变副本，然后再进行更改。

• 项目（NSDictionary）
  • 项目（NSDictionary）
    • aString: NSString
    • aString2：NSString
    • 日期：NSDate
    • aDate2：NSDate
    • aBool: BOOL
    • aTI1：NSTimeInterval
    • aTI2：NSTimeInterval
    • 关键字 (NSArray)
      • 关键字：NSString
      • 关键字：NSString

Answer 1

几年前，我出于完全相同的原因编写了一些类别方法，将整个用户默认树转换为可变的。它们就在这里——使用它们需要您自担风险！ :-)

//
//  SPDeepCopy.h
//
//  Created by Sherm Pendley on 3/15/09.
//

#import <Cocoa/Cocoa.h>

// Deep -copy and -mutableCopy methods for NSArray and NSDictionary

@interface NSArray (SPDeepCopy)

- (NSArray*) deepCopy;
- (NSMutableArray*) mutableDeepCopy;

@end

@interface NSDictionary (SPDeepCopy)

- (NSDictionary*) deepCopy;
- (NSMutableDictionary*) mutableDeepCopy;

@end

---

//
//  SPDeepCopy.m
//
//  Created by Sherm Pendley on 3/15/09.
//

#import "SPDeepCopy.h"


@implementation NSArray (SPDeepCopy)

- (NSArray*) deepCopy {
    unsigned int count = [self count];
    id cArray[count];

    for (unsigned int i = 0; i < count; ++i) {
        id obj = [self objectAtIndex:i];
        if ([obj respondsToSelector:@selector(deepCopy)])
            cArray[i] = [obj deepCopy];
        else
            cArray[i] = [obj copy];
    }

    NSArray *ret = [[NSArray arrayWithObjects:cArray count:count] retain];

    // The newly-created array retained these, so now we need to balance the above copies
    for (unsigned int i = 0; i < count; ++i)
        [cArray[i] release];

    return ret;
}
- (NSMutableArray*) mutableDeepCopy {
    unsigned int count = [self count];
    id cArray[count];

    for (unsigned int i = 0; i < count; ++i) {
        id obj = [self objectAtIndex:i];

        // Try to do a deep mutable copy, if this object supports it
        if ([obj respondsToSelector:@selector(mutableDeepCopy)])
            cArray[i] = [obj mutableDeepCopy];

        // Then try a shallow mutable copy, if the object supports that
        else if ([obj respondsToSelector:@selector(mutableCopyWithZone:)])
            cArray[i] = [obj mutableCopy];

        // Next try to do a deep copy
        else if ([obj respondsToSelector:@selector(deepCopy)])
            cArray[i] = [obj deepCopy];

        // If all else fails, fall back to an ordinary copy
        else
            cArray[i] = [obj copy];
    }

    NSMutableArray *ret = [[NSMutableArray arrayWithObjects:cArray count:count] retain];

    // The newly-created array retained these, so now we need to balance the above copies
    for (unsigned int i = 0; i < count; ++i)
        [cArray[i] release];

    return ret;
}

@end

@implementation NSDictionary (SPDeepCopy)

- (NSDictionary*) deepCopy {
    unsigned int count = [self count];
    id cObjects[count];
    id cKeys[count];

    NSEnumerator *e = [self keyEnumerator];
    unsigned int i = 0;
    id thisKey;
    while ((thisKey = [e nextObject]) != nil) {
        id obj = [self objectForKey:thisKey];

        if ([obj respondsToSelector:@selector(deepCopy)])
            cObjects[i] = [obj deepCopy];
        else
            cObjects[i] = [obj copy];

        if ([thisKey respondsToSelector:@selector(deepCopy)])
            cKeys[i] = [thisKey deepCopy];
        else
            cKeys[i] = [thisKey copy];

        ++i;
    }

    NSDictionary *ret = [[NSDictionary dictionaryWithObjects:cObjects forKeys:cKeys count:count] retain];

    // The newly-created dictionary retained these, so now we need to balance the above copies
    for (unsigned int i = 0; i < count; ++i) {
        [cObjects[i] release];
        [cKeys[i] release];
    }

    return ret;
}
- (NSMutableDictionary*) mutableDeepCopy {
    unsigned int count = [self count];
    id cObjects[count];
    id cKeys[count];

    NSEnumerator *e = [self keyEnumerator];
    unsigned int i = 0;
    id thisKey;
    while ((thisKey = [e nextObject]) != nil) {
        id obj = [self objectForKey:thisKey];

        // Try to do a deep mutable copy, if this object supports it
        if ([obj respondsToSelector:@selector(mutableDeepCopy)])
            cObjects[i] = [obj mutableDeepCopy];

        // Then try a shallow mutable copy, if the object supports that
        else if ([obj respondsToSelector:@selector(mutableCopyWithZone:)])
            cObjects[i] = [obj mutableCopy];

        // Next try to do a deep copy
        else if ([obj respondsToSelector:@selector(deepCopy)])
            cObjects[i] = [obj deepCopy];

        // If all else fails, fall back to an ordinary copy
        else
            cObjects[i] = [obj copy];

        // I don't think mutable keys make much sense, so just do an ordinary copy
        if ([thisKey respondsToSelector:@selector(deepCopy)])
            cKeys[i] = [thisKey deepCopy];
        else
            cKeys[i] = [thisKey copy];

        ++i;
    }

    NSMutableDictionary *ret = [[NSMutableDictionary dictionaryWithObjects:cObjects forKeys:cKeys count:count] retain];

    // The newly-created dictionary retained these, so now we need to balance the above copies
    for (unsigned int i = 0; i < count; ++i) {
        [cObjects[i] release];
        [cKeys[i] release];
    }

    return ret;
}

@end

Answer 2

我认为这样的事情应该有效。

NSData *buffer;
NSMutableDictionary *_dict1, *_dict2;

// Deep copy "all" objects in _dict1 pointers and all to _dict2  
buffer = [NSKeyedArchiver archivedDataWithRootObject: _dict1];  
_dict2 = [NSKeyedUnarchiver unarchiveObjectWithData: buffer];  

Answer 3

进行深度复制的简单方法是使用 CFPropertyListCreateDeepCopy。下面是示例（使用 ARC）：

    NSDictionary *newDictionary =
 (__bridge NSDictionary *)(CFPropertyListCreateDeepCopy(kCFAllocatorDefault,
         (__bridge CFPropertyListRef)(originalDictionary),
          kCFPropertyListImmutable));

本示例中的原始字典是 NSDictionary

CFPropertyListRef，只要 CFPropertyListRef 的顶级实体是 CFDictionary，就可以简单地转换为 NSDictionary。

Answer 4

如果有人想要可变副本，请使用以下代码：

NSMutableDictionary *newDictionary = (NSMutableDictionary *)CFBridgingRelease(CFPropertyListCreateDeepCopy(kCFAllocatorDefault, (CFDictionaryRef)dict, kCFPropertyListMutableContainers));